1. Field of the Disclosure
Embodiments of the invention relate to a liquid crystal display and a method of driving the same.
2. Discussion of the Related Art
Active matrix type liquid crystal displays display a motion picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal displays have been implemented in televisions as well as display devices in portable devices such as office equipments and computers, because of the thin profile of the active matrix type liquid crystal displays.
Liquid crystal cells of the liquid crystal display change a transmittance by a potential difference between a data voltage supplied to a pixel electrode and a common voltage supplied to a common electrode, thereby displaying an image. The liquid crystal display is generally driven in an inversion scheme of periodically inverting a polarity of the data voltage applied to liquid crystal cell so as to prevent deterioration of the liquid crystal. When the liquid crystal display is driven in the inversion scheme, the image quality of the liquid crystal display may be reduced depending on a correlation between the polarities of the data voltages charged to the liquid crystal cells and a data pattern of an input image. This is because the polarities of the data voltages charged to the liquid crystal cells are not balanced between the positive and negative polarities and one of the positive and negative polarities becomes dominant. Hence, the common voltage applied to the common electrode shifts. When the common voltage shifts, a reference potential of the liquid crystal cells swings. Therefore, this may cause an observer to sense a crosstalk, a flicker, or a smear in an image displayed on the liquid crystal display.
FIG. 1 shows data examples of problem patterns which may result in a reduction of the image quality of a liquid crystal display when the liquid crystal display is driven in a dot inversion scheme.
As shown in FIG. 1, among the problem patterns, a pattern in which (white) pixel data of a white gray level and (black) pixel data of a black gray level alternate every one pixel is referred to as a shutdown pattern. Each pixel data includes red subpixel data R, green subpixel data G, and blue subpixel data B. The shutdown pattern may be detected by counting shutdown patterns included in an input image and determining whether or not the data of the input image is the shutdown pattern based on the count value. For example, when Nth (N is a positive integer) pixel data is pixel data of the white gray level and (N+1)th pixel data is pixel data of the black gray level, a count value of a problem pixel counter increases by 1. When the count value is equal to or greater than a predetermined threshold value, the data of the input image is decided as the shutdown pattern.
As shown in FIG. 2, it is necessary to previously define a maximum number of patterns (i.e., (23−1)·2=14) that may appear in six subpixels, so as to recognize the shutdown pattern. Further, a detection logic module for detecting each of the 14 patterns is required.
The problem patterns include various patterns resulting in the reduction of the image quality in the dot inversion scheme as well as the shutdown pattern. Examples of the problem patterns include a smear pattern and a flicker pattern as shown in FIG. 12.
If the flick er pattern is recognized from the input image, a method capable of preventing the flicker by changing the inversion period of the polarity in the dot inversion scheme may be considered. One example of the method is disclosed in disclosed in detail in U.S. patent application Ser. No. 12/830,971, Publication No. US 2011/0037760 A1 corresponding to Korean Patent Application No. 10-2009-0075382 filed Aug. 14, 2009, which are hereby incorporated by reference in their entirety. However, in the method, when the dot inversion scheme is changed through the recognition of the flicker pattern, the flicker does not appear. Therefore, it is difficult to decide the shift of the common voltage. Accordingly, when the flicker pattern is input, it is difficult to determine a shift degree of the common voltage in a common voltage tuning process if the dot inversion scheme is changed. Therefore, it is difficult to optimize the common voltage.